Field of the Invention
Embodiments of the present invention relate to millimeter-wave modulation apparatuses, and more particularly, to a low power and high efficiency millimeter-wave modulation apparatus capable of modulating digital data to a transmitting signal in a millimeter frequency band.
Description of the Related Arts
According to the exhaustion of radio frequency resources used in communication, worldwide interest has been on utilization of a millimeter wave band. When a millimeter wave band is used, it is advantageous in that the millimeter wave band can be used in existing other radio communication systems without interference, and giga radio systems can be easily established even when a communication technique having low frequency efficiency is used. In particular, as it a micro process of a CMOS (Complementary Metal Oxide Semiconductor), which is a standard process technique for semiconductors, has become a possibility even under a technical condition of 100 nm or less, a transmitter-receiver in a millimeter wave band may enable an RF circuit in a band of 60 GHz to be easily implemented. Thus, utilization the millimeter wave band in communications has been promoted.
FIG. 1 is an exemplary view showing a structure of a conventional millimeter transmitter.
The millimeter transmitter illustrated in FIG. 1 has a structure in which path I and path Q are made in order to put many pieces of communication information in the same frequency resource; a signal modulated in a digital circuit is up-converted into a millimeter frequency through a digital analogue converter (DAC) and an I/Q mixer; and amplified power of the power amplifier is finally controlled for enabling transmission to a desired communication distance.
In this case, in order to increase frequency efficiency, complicated digital modulation methods is used. Various methods, such as from a QPSK (Quadrature Phase Shift Keying) method to a 64QAM (Quadrature Amplitude Modulation) method, are applied. However, it is problematic in that a PARR (Peak to Average Power Ratio) required by a modulation method becomes higher as a level of the modulation method becomes gradually higher. In terms of the power amplifier, this may be interpreted to the extent that the power amplifier (PA), which is a final output terminal, provides back-off power.
Currently, in a frequency band of 3˜4 GHz, a PAPR is about 8 dB, and the power amplifier is used by providing back-off power to the extent of 8 dB. In particular, such a system causes a more problem in a millimeter wave band. This is because the efficiency of a power amplifier used in a millimeter frequency is remarkably reduced compared to that of a power amplifier used in a frequency of 3˜4 GHz. Furthermore, when high back-off power is applied, power consumed by the millimeter power amplifier is mostly consumed as heat so that entire efficiency of the transmitter is rapidly reduced.
FIG. 2 is an exemplary view showing a structure of a conventional millimeter-wave OOK modulation.
The millimeter-wave transmitter illustrated in FIG. 2 has an OOK (On-off Keying) structure and may carry out a very simple modulation by turning on or off a mixer or a power amplifier. Thus, it has a structure suitable for a system in which a power amplifier increases the efficiency of output power by minimizing a PAPR, thereby facilitating transmission with lower power. However, the millimeter OOK modulation apparatus having such a structure is disadvantageous in that frequency efficiency is not maximized, the efficiency of power compared with modulation is not high, and the apparatus is vulnerable to noise because it includes amplitude information.
FIG. 3 is a partial exemplary view showing a structure of a conventional millimeter-wave array transmitter.
In the millimeter-wave array transmitter illustrated in FIG. 3, the size of an antenna becomes small due to a short wavelength, and as a result, it is advantageous in that an array is easily performed compared to a 3G or 4G system. In addition to this, power, which cannot be obtained by a single power amplifier, may be obtained by several power amplifiers. That is, a method of obtaining a high output by combining the power of several power amplifiers in the air provides many advantages in establishing millimeter systems. Despite the fact that a currently used array transmitter structure has only an advantage that a power amplifier outputs low power because a modulated signal is applied to the power amplifier in a state of being power-distributed and being phase-shifted, the structure has a limit that there is no improvement in terms of efficiency.